A low-pressure centrifugal chiller vessel has many commercial and industrial applications, such as providing air conditioning to hotels, cooling fluid to a manufacturing process, or commercial food refrigeration. Inherent to their use is an expectation that these systems will have a minimal amount of down time. Low-pressure centrifugal refrigeration systems are typically operated without maintenance until a breakdown occurs, and only then is any repair/maintenance service performed. The down time that results from this kind of reactive maintenance program is, at best, an inconvenience for the user. But frequently the down time can also have costly consequences, such as food spoilage if the application is commercial food refrigeration.
A mechanical refrigeration system with a low-pressure centrifugal chiller vessel typically uses a chlorofluorocarbon (CFC) refrigerant. Some typical CFC refrigerants are those sold by DuPont under the trademark FREON. CFC refrigerants vary by boiling point; for example, some rather common CFC refrigerants are R-11, R-113, and R-123. These as well as other CFC refrigerants are well-known and widely used as heat transfer media in mechanical refrigeration.
Refrigeration systems generally require the pressurized storage of a vaporized refrigerant. For example, a low-pressure centrifugal chiller vessel generally operates under a vacuum of about sixteen inches of mercury, and should not operate at a pressure exceeding fifteen pounds per square inch above atmospheric pressure. To comply with applicable safety codes in this regard, these systems have a pressure relief system to vent a storage vessel that becomes over-pressurized. For many years, it was the practice in industry to design the relief system to vent the CFC refrigerant from the over-pressurized storage vessel directly into the atmosphere. Recently; however, because of concerns for the possible destruction of the ozone layer above the earth, it has become desirable, and in some cases mandatory, to minimize the release of CFC refrigerants. And environmental concerns, though sufficient, are not the only factor in favor of preventing the loss of CFC refrigerants. The cost of CFC refrigerants has escalated drastically, which in some cases has risen over ten fold in only the past few years.
Hence, it has become industry practice to add a mechanical, normally closed, re-seating relief valve to the pressure relief system of most mechanical refrigeration systems to minimize the amount of CFC refrigerant that may be vented into the atmosphere during an over pressure condition. This valve is placed in series downstream from a fragmentary carbon rupture disk. The fragmentary carbon disk is calibrated to burst into pieces at a predetermined maximum pressure. At any pressure up to the maximum pressure, the carbon rupture disk provides an excellent positive seal to prevent the venting of CFC refrigerant and the infiltration of any contaminants into the refrigeration system. The combination of the fragmentary carbon rupture disk and the mechanical, normally closed, re-seating relief valve, provides the positive seal characteristics of the carbon rupture disk and a method to close the relief vent to retain the CFC refrigerant once the disk has burst and the overpressure condition has passed.
A common limitation of refrigeration systems having a mechanical re-seating relief valve downstream from a fragmentary carbon rupture disk is that the fragments from the burst carbon rupture disk often lodge in the valve seat of the relief valve. Naturally, any debris or fragments of significant size that lodge in the seat will interfere with the relief valve's ability to later close, and absent the positive seal that is normally provided by a mechanical re-seating relief valve, the CFC refrigerant would continue to vent into the atmosphere.
Many designers of refrigeration systems have attempted to overcome this common limitation by utilizing a non-fragmentary, metal rupture disk in place of a fragmentary carbon disk. The use of the metal rupture disk does prevent fragments of the burst rupture disk from interfering with the re-seating of the mechanical relief valve. However, the metal disk leaves unsolved a litany of other problems and creates a particularly undesirable consequence of its own. For example, one limitation of many metal rupture disks pertains to the bent metal from the rupture disk disturbing the fluid flow characteristics of the exiting fluid that can interfere with the operation of the mechanical relief valve.
As a result, there is a need for a rupture disk that does not interfere with the operation of a downstream mechanical relief valve. The present invention is one solution that satisfies this need in a novel and unobvious way.